The invention relates to an electron spin resonance device, and more particularly to an electron spin resonance device having a microwave circuit for detecting an electron resonance.
A typical structure of a microwave circuit for a conventional electron spin resonance device will be described with reference to FIG. 1. In the conventional electron spin resonance device, a microwave power is supplied into a wave-guide by a gun oscillator 12 which is driven by a power supply 10. The microwave power is transmitted though an uni-guide 14 and a directional coupler 16 to a wave-guide attenuator 18 which so adjusts the microwave power as to have an electric energy being suitable for a resonance condition of a measuring sample S. Such microwave power suitable adjusted is subsequently transmitted through a circulator 20 to a cavity resonator 22. In the cavity resonator 22, the microwave power is added into a measuring sample S which is arranged along a direction of a microwave magnetic field in the cavity resonator 22. A polarization magnetic field being perpendicular to the microwave magnetic field is applied by a pair of magnets 24.
When the measuring sample S is measured in the cavity resonator 22, the polarization magnetic field B.sub.0 is sweeped. The electron resonance appears in the measuring sample only when the following condition is satisfied. EQU h=g.beta.B.sub.0 ( 1)
h: Planck's constant PA1 .sqroot.: resonance frequency PA1 g: Lande factor PA1 .beta.: Bohr magnetor PA1 F1, F2, . . . Fn: noise factor on each stage. PA1 G1, G2, . . . Gn: the amplification grade on each stage.
If the electron resonance appears, a reflective output of a resonance signal from the cavity resonator 22 results.
Then, the resonance signal is transmitted again through the circulator 20 to a magic-T 26 which has both E-branch and H-branch. The resonance signal is transmitted through the E-branch of the magic-T 26 to a pair of crystal detectors 28 and 30 which are arranged at opposite sides of a balanced branch at the magic-T 26. The resonance signals supplied to the crystal detectors 28 and 30 have the same amplitude and inversive phases. The magic-T 26 at its H-branch is supplied from the directional coupler 16 through two coaxial waveguide convertors 34 and 36 with a part of the microwave power as a reference signal for such homodyne detection. The resonance signal is thus hybridized with the reference signal for a subsequent detection.
Detection outputs from the both crystal detectors 28 and 30 of the magic-T 26 are respectively added with the in-phase reference signal and the anti-phase resonance signal. As a result, each of the above detection outputs is subjected to a differential amplification by a preamplifier 38 for addition of resonance signal components but cancellation of reference signal components thereby the resonance signal component only remains.
On the other hand, the polarization magnetic field B.sub.0 receives a modulation of the magnetic field with a modulation frequency f.sub.m. The above microwave detection performance makes the preamplifier 38 amplify only the modulation frequency component for a subsequent transmission to a main amplifier which is not illustrated. The main amplifier conducts a narrow band amplification of a center frequency f.sub.m for such a subsequent phase detection that the above center frequency f.sub.m serves as a reference frequency thereby the electron spin resonance signals as a direct output are obtained.
A sensitivity of a detection of the electron spin resonance signal is associated with a general noise factor F. In a case of the detection by multi-stage receiving system, the general noise factor F is given by the following equation. EQU F=F1+(F2-1)/G1+(F3-1)/G1G2,++(Fn-1)/G1,G2,Gn-1 (2)
In the prior art, the electron spin resonance signal is detected by the cavity resonator 22 and transmitted through the circulator 20 for a receipt of diode detection by the crystal detectors 28 and 30 and a subsequent transmission to the preamplifier 38. That is why the sensitivity of the resonance signal detection is defined by the noise factor and the amplification grade of the detection diode.
The sensitivity of the resonance signal detection will be described with reference to numerical values when a Schottky barrier diode is used on a detecting stage. On the assumption that the noise factor F1 and the amplification grade G1 of the detector are 6 dB and -5 dB respectively (an amplification grade of approximately 0.3 times) and the noise factor of the signal amplifier F2 is 4 dB, the noise factor of the receiving system will be expressed as follows. ##EQU1##
In is apparent that in the prior art the noise factor of the receiving system is extremely high which teaches that the sensitivity of the resonance signal detection is undesirable.